VOIP presentation by 0s7iRTF


									VoIP - ENUM

  CS 412
Presented by:
ChunLok Mah
                              VoIP Introduction

1) (VoIP) Voice over IP / IP Telephony
   Refers to the technology that supports two-way transmission of voice traffic
   over a packet-based IP network.

2) IP Phone, Web Set, or Soft Phone – new digital phone sets that utilize the
   VoIP technology. A Soft Phone typically does not include a traditional desktop
   phone, but instead uses the computer monitor of a local pc as the phone.

3) IP Telephony Gateway – device that translates IP telephone calls to the
   standard signal based telephone network, or vice versa. This allows users of
   IP phone systems to communicate with people using traditional phone

4) Integrated Communication Platform (Gatekeeper)– device that combines all
   of a small businesses’ communication needs into one box. Serves as the
   hub/router for your local area network, connects with your DSL, cable, or T1
   line as your gateway to the web, and provides your IP telephony services.

5) Multi-Service Networking – refers to putting all of the major communications
   services – voice, video, and data – onto a single IP based network.
Public switched telephone network (PSTN)


   Voice Over IP (VoIP)

data network

                          H.323 = Packet-based
       VoIP   PSTN

 HighSpeed                 PBX
data network           interconnect
               VOIP   PSTN (continue)

 HighSpeed                                    PBX
data network                              interconnect
                      VoIP   PSTN (continue)

                                    3) Gateway looks up
5) Bob IP telephone
                                       database with query
  send corresponding                   Gateway selects server
  telephone call code        

      4) Gateway completes cal to SIP
         port on server
                                                            2) Telephone network routes
                                                               the call request to the
                                                               associate IP Gateway

                                   1) Alice dials Bob’s telephone
                                      number +61012345678
                       VOIP   PSTN (example)
Consider an example. When Alice, on a normal telephone, wants to call
Bob, on an Internet phone.

1. All Alice needs to do is simply dial Bob’s telephone number, or his E.164
2. Of course, because Bob’s phone is connected to the Internet and can’t directly
   receive Alice’s call request, a gateway is necessary. The telephone system
   should be able to map Alice’s call request to the Internet telephony gateway
   that is configured to act as Bob’s gateway agent.
3. The gateway then needs to translate Bob’s E.164 phone number into an IP
   address. Then the gateway has to map the telephone network signals
   associated with Alice’s call request to corresponding signals within an Internet
   session initiation protocol,
4. and then send these IP packets to Bob’s Internet phone. If Bob answers the
   call, the phone uses the same protocol to inform the gateway
5. The gateway then sends a corresponding telephone call code across the
   telephone network to Alice.

   When Bob accepts the call, the gateway can then pass all data originating
from Alice to Bob’s IP address, and all data received from Bob’s IP address
across to the telephone connection to Alice for the duration of the call.
   Alice never needs to know that Bob is using an Internet device. Alice dialed a
phone number, heard it ring, and then heard Bob answer the call. For Alice,
nothing has changed. Bob heard the phone ring, picked it up, and talked to Alice.
For Bob, nothing has changed.
                          VOIP   PSTN (problem)

    The simplest way to configure each gateway is to load each gateway with a configured
list of E.164 phone numbers and corresponding IP addresses. This approach is currently
very common, but, like all statically configured approaches, has its weaknesses. But what
happens when the IP device is numbered dynamically using the Dynamic Host Configuration
Protocol (DHCP), or if it’s mobile, and moves from one service provider’s IP network to
another, or when the end subscriber changes providers and that subscriber’s network is
renumbered, or when the primary gateway fails and the providers want to switch to a
secondary device? In other words, how can this mapping be dynamic rather than static?

    The way a dynamic domain name-to-IP address mapping can be maintained on the
Internet is through the Internet Domain Name System (DNS). The telephony gateway can
use the E.164 address as the DNS query, and request the DNS to return the corresponding
IP address. In our example, when Alice rings Bob, the gateway can use the DNS to obtain
Bob’s current IP address. The gateway can then use the Session Initiation Protocol (SIP) to
send to Bob’s Internet phone a call request, which then starts Bob’s phone ringing. If Bob
changes IP address, then the corresponding change is a change in the DNS, not in the
gateway itself. If the primary gateway fails and a secondary gateway is used, the secondary
system can already access all necessary mappings through the DNS. The solution of this
critical job fall to a little-known standard called Enum
                      What is ENUM?

 Short for “electronic numbering”.
 A protocol developed by the Internet Engineering Task Force
 Allows telephone numbers to be mapped to Internet Protocol
  (IP) addresses. Through this mapping, a calling user can use
  the domain name system (DNS) to identify all communications
  services, such as facsimile, email, VoIP (voice over Internet
  Protocol) and a mobile phone service associated with the called
 Internet telephony will benefit from this technology. It is being
  sought by federal agencies and other large organizations that
  see many potential benefits in the technology, such as big cuts
  in long-distance phone bills.
 Telephone numbers used in ENUM would be E.164 numbers.
  These are telephone numbers defined and structured at the
  international level by the International Telecommunication Union
  (ITU) in its E.164 recommendation. E.164 describes the
  structure of the numbers used in the international
  telecommunication system and defines the general framework
  and criteria for assigning country codes (eg. 61 for Australia).
                     How does ENUM work?

1) Once a telephone number is entered, it is translated into an Internet
   address using the following steps:
2) The phone number is translated into a fully qualified E.164 number
   by adding the city (or area) and country code. Example: 555-1234
   dialed in Washington, DC becomes +1-202-555-1234, where the "1"
   represents the North American country code. The "+" indicates that
   the number is a fully qualified E.164 number.
3) All characters are removed except for the digits. Example:
4) The order of the digits is reversed. Example: 43215552021
5) Dots are placed between each digit. Example:
6) The domain "e164.arpa" is appended to the end. Example:
7) ENUM then issues a DNS query on this domain. Once the
   authoritative name server is found, ENUM retrieves relevant NAPTR
   Resource records and will perform according to the user's registered
   services for that number.
                      Enum - arpa

What is .arpa, and why is it the top level domain for
ENUM? Why not create a new top-level domain
specifically for ENUM?

The .arpa domain has been designated for Internet
infrastructure purposes. It is managed by the Internet
Assigned Numbers Authority (IANA) in cooperation with the
Internet technical community under the guidance of the
Internet Architecture Board (IAB). A new top-level domain
(e.g., .e164) was not created because ENUM is an
infrastructure application appropriate for designation within
the previously established .arpa domain. ENUM is
considered appropriate as an infrastructure application
because it provides a set of DNS-based resource directories,
referenced by phone number, for use by various ENUM-
enabled application clients (such as telephones, SIP servers,
and voice messaging systems).
           Why is the number reversed?

   DNS names are structured from right to left. In the
example used above
(, DNS would first
search for the top-level domain arpa, then search
second-level domains for e164, then search the next
level for the country code 1, etc.
                                  Enum (example)

Let’s say Bob’s Internet telephone services are mapped to the E.164 address

1) All Alice needs to do is simply dial Bob’s telephone number, or his E.164
2) The telephone network routes the call request toward the Internet
   gateway that is the nominated service agent for this E.164 number.
3) The Internet gateway takes the call setup request with Bob’s number and
   first reverses the digits, then inserts a “.” between each digit, and finally
   appends e164.arpa. The resultant DNS string is the fully qualified
   domain name This name is then
   passed as a query to the Enum DNS.
4) The Enum DNS will reply with all associated NAPTR DNS resource records
   IN NAPTR = 100 10 "u" "sip+E2U" "!^.*$!sip:bob@sip.telebob.au!"
5) The Internet gateway will then query for the IP address for
   sip:bob@server from DNS server
6) The DNS will reply with the IP
7) Gateway will completes call to IP port on server
8) Bob picks up the phone. The gateway( then opens up a session
   with UDP port 5060 on this SIP server to complete the call setup,
   requesting a voice session with the user Bob on this server.
                               Enum (example)

8) Bob IP telephone
                                         6) Response
                                         5) Query IP address of server
       7) Gateway completes              4) Response sip+E2U sip:bob@server
          call to IP port on
          server                3) Gateway queries

                                                       2) Telephone network routes
                                                          the call request to the
                                                          associate IP Gateway

                                                       1) Alice dials Bob’s telephone
                                                          number +61012345678
                        Enum - (NAPTR)
100 10 "u" "sip+E2U" "!^.*$!sip:bob@sip.telebob.au!"
100 10 "u" "mailto+E2U" "!^.*$!mailto:bob@mail.pobob.au!"

  (a)       (b)      (c)                           (d)

  (a) Order Value - In this case the DNS entry uses an order value of 100 and a
                              preference of 10.
  (b) Rule - The “u” flag indicates that the rule is terminal and that the
                  URI is to be used.
  (c) Call request - the gateway picks the sip service
                  The gateway then opens up a session with UDP port 5060 on
      this SIP
                  server to complete the call setup, requesting a voice session
      with the
                  user Bob on this server.

                  The gateway can complete the original text message delivery
                  by opening a TCP session on port 25 of the mail server and
                  the message as mail addressed to user bob@mail.pobob.au.
  (d) URL - The operation of the regular expression produces the URI of the

1) Enum has the ability to make end-to-end phone calls using only regular data
   networks and avoiding the phone network entirely
2) "Enum standardizes the way in which you actually dial a phone number over
   the Internet without having to go to the PSTN for translation services" to an
   IP address, said David Fraley, principal analyst with Gartner Inc.'s Dataquest
   unit in San Jose, Calif. "Enum is a major step in helping to deliver voice-data
   convergence on an IP network."
3) That's the promise of Enum on a basic, though important, network plumbing
   level. From the users' perspective, Enum would let people give out a single
   telephone number, yet have it connect to multiple IP-enabled
   communications devices, such as their telephone, wireless phone, e-mail
   client, fax machine and wireless handheld computer.
4) "One thing Enum solves is the "business card' problem of too many
   addresses.... Over time you'll see people using a single telephone number as
   an address for a Web page or an e-mail address, or to receive a fax or an
   instant message," said Tom McGarry, chief of strategic technical initiatives at
   NeuStar Inc., Washington, D.C., one of three companies testing an Enum
   registry database.

1) (Enum) – Electronic Numbering
2) (PBX) - Private branch exchange service
3) (PSTN) - Public switched telephone network
4) (SIP gateway) - Session Initiation Protocol gateway
5) (NAPTR) - Naming Authority Pointers records.

1) http://www.cisco.com/warp/public/759/ipj_5-2.pdf
2) http://www.tldp.org/HOWTO/VoIP-HOWTO-3.html#ss3.1
3) http://www.networkcomputing.com/918/918f1.html
4) http://www.enum.org/
5) http://www.epic.org/privacy/enum/default.html
6) http://www.upgradepress.com/topstories/0602_voipterms.htm
7) http://www.enum.org/information/faq.cfm

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